Energy consumption has long been an important issue for mobile terminals in cellular systems. Recent trends in green technology make it important to reduce the energy consumption also for the base stations (BS or NodeB, eNodeB) as the base station power consumption is a non-negligible part of the cost for the operator and excessive power consumption has a negative impact on the environment. Furthermore, the energy consumed as part of the base station operation generates heat, and active cooling (air conditioning) is typically required to control the temperature of the equipment. Active cooling will further add to the total energy consumption of a base station site. Unlike terminals, which can go into idle (or sleep) mode when they are not active, base stations need to transmit pilots, synchronization symbols and broadcast messages in order for camping terminals to be in sync with the network.
A prior art solution for reducing the overall energy consumption in the network is to, in case of low load (for instance during the night), let certain base stations go into an idle mode and rely on enlarged neighboring cells to serve the area normally covered by the now idle base station.
A drawback of the prior art solution is that when a number of terminals start to require significant amounts of resources, then the network does not have any information on which terminals should be handled by the active base stations and which terminals should be handled by the awakened base stations. Thus, it is not possible to tell whether awakening of one or more of the idle base stations would actually be of any help for the active base stations.